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Old 07-26-2013, 07:55 PM #1
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MilchstrabeStern MilchstrabeStern is offline
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Default Arduino for current control

I have a project that requires the use of a green laser for aligning some equipment. The laser I am using is, I believe, this one, but was purchased off Amazon at the time:

Aliexpress.com : Buy Free Shipping Green Beam Laser Pointer Pen High Power Bright 500 10000M +Free Battery+Free Charger from Reliable High Quality green laser suppliers on HK ZBTECH Co.,Ltd.

Unfortunately it drains the 3.7 16340 pretty quick and has become unreliable in that regard. Since this project involves the use of other electronics and and Arduino, I already will have a power supply hooked up, it's just a matter of connecting the laser. However, the power supply is still going to be a battery (portability is paramount).

For efficiency reasons, I decided I'd limit the current to the diode, but didn't want to remove/modify the driver board. I decided to just connect the diode to an NPN transistor, and then drive the transistor with the Arduino. Essentially I'm chopping the current to the laser driver, and in turn, the laser. I'm bit banging, so nothing fancy. I'll do:

on 1ms -- off 30ms -> very dim
on 1ms -- off 1-3ms -> beam visible in a lit room
on 1ms -- off 0ms -> full blast baby

A potentiometer serves to adjust between dim and bright.

For my application, this method works just fine. The strobe effect during movement is not important to me. However, I worry that I could damage the drive circuit with so many repeated on/off cycles. Is this a valid concern? Also, I'm feeding the driver 5V from a 7805 voltage regulator -- obviously higher than the 3.7V battery. Although the laser driver still outputs 1.8V, am I within the operating range of the components likely used on this board? The only one I could easily identify was a LM358 voltage comparator/op amp.

I would also love to hear suggestions for better ways to current control the diode without swapping in a new driver board. However, I would like to retain the ability to adjust the current for different situations easily. Compactness is not an issue. I have wires coming from the laser assembly to a control board.

Thanks!



Last edited by MilchstrabeStern; 07-26-2013 at 08:01 PM.
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